AUGUSTA, Maine — John Richardson, a former speaker of the House and economic development commissioner in the Baldacci administration, became the latest person to join the crowded field of candidates hoping to become Maine’s next governor.

Richardson formally announced his candidacy on Monday, although he has been discussed for months as a likely contender for the Democratic nomination.

Richardson, 52, resigned from his position as commissioner of the Department of Economic and Community Development in order to campaign for governor. Deputy Commissioner Thaxter Trafton was named acting commissioner on Monday.

Richardson joins more than 20 other candidates — including seven other Democrats, six Republicans and two Green Independents — who have filed paperwork indicating plans to run for the Blaine House in November 2010.

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Richardson pledged to focus on job development, making government more efficient and effective, and capitalizing on Maine’s natural resources to help the state recover from the recession.

“This state’s economy was once built on exploiting those resources,” Richardson said in prepared remarks. “Its future will be built on harnessing and preserving them. I offer Maine people a comprehensive vision for bringing together economic development, environmental protection and renewable energy.”

A lawyer, Richardson served in the Maine House of Representatives from 1998 to 2006, the last two years as speaker.

In addition to Richardson, there are two other former House speakers running as Democrats: former Attorney General Steven Rowe and Elizabeth “Libby” Mitchell, who presides as Senate president.

The other Democrats who have filed paperwork with the Maine Commission on Governmental Ethics and Election Practices are Donna Dion of Biddeford, Rep. Dawn Hill of York, Eriq Manson of Old Orchard Beach, Rosa Scarcelli of Portland and Peter Truman of Old Orchard Beach.